Nitrogen-free corrosion inhibitors having a good buffering effec

Details Nitrogen-free corrosion inhibitors having a good buffering effec Nitrogen-free corrosion inhibitors having a good buffering effec

1997-06-16

1998-08-18

Green, Anthony

Compositions: coating or plastic

Coating or plastic compositions

Corrosion inhibiting coating composition

106 1413, 106 1443, 252393, 252395, 252396, 422 17, C23F 1112, C23F 1110

Patent

active

057953724

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to corrosion control formulations in the form of an aqueous emulsion or preferably an aqueous solution for temporarily protecting metal surfaces, more particularly iron-containing surfaces, against corrosion. To avoid wastewater pollution, they are free from nitrogen and are distinguished by a good buffering effect so that, despite the possible introduction and/or microbiological production of acids, their alkaline pH value can be maintained for prolonged periods.
2. Discussion of the Related Art
The protection of metals susceptible to corrosion, for example iron, aluminium, zinc, copper or their alloys, against corrosion is a widespread technical problem. It arises in particular when the metal parts are not, or not yet, covered with a permanently corrosion-inhibiting coating, for example in the form of a paint, on account of the particular condition in which they are being treated or on account of their particular field of application. Examples of this are metal parts involved in technical treatment stages such as, for example, machining or forming or cleaning and assembled metal components such as, for example, heat exchangers or pipelines which come into contact in service with corrosive aqueous media. In order to prevent or inhibit corrosion during or between the individual treatment steps or during the intended use, the metal surfaces are contacted with corrosion inhibitors which provide temporary protection against corrosion. It is often necessary for technical reasons, for example in water-based cooling or heating circuits, or desirable in the interests of pollution control, for example during or after cleaning of the metal surfaces with water, that the metal surfaces be contacted with the corrosion inhibitors in the form of an aqueous phase. Accordingly, a desirable property of corrosion inhibitors is that they should be soluble or at least dispersible in water.
Various inorganic and organic compounds are known as water-soluble or water-dispersible corrosion inhibitors. Inorganic corrosion inhibitors can be based, for example, on chromates, nitrites or phosphates which, unfortunately, are more or less toxicologically and ecologically unsafe. Organic corrosion inhibitors are frequently based on carboxylates, amines, amides or on nitrogen-containing heterocyclic compounds. There are serious toxicological objections to the use of secondary amines or compounds capable of releasing secondary amines on account of the possibility of nitrosamine formation. However, other nitrogen-containing compounds are toxicologically unsafe or at least problematical on account of the risk of water pollution. Although carboxylic acids do not have any of these disadvantages, they do not show adequate long-term activity in practice when the pH value of the inhibitor baths is reduced by the introduction of acid or by microbiological processes to such an extent that the carboxylic acids are present not in the salt form, but in the less effective acid form.
EP-B-341 536 describes a water-soluble corrosion inhibitor system containing alkenyl succinic acid, aryl sulfonyl anthranilic acid and alkanolamines. This system does not satisfy the nitrogen-free requirement. GB-B-1,238,205 describes a water-soluble corrosion-inhibiting combination consisting of gluconate and benzoate or salicylate salts. On account of the extremely hydrophilic character of the salts used, this combination is limited in its effectiveness. EP-A-294 649 teaches the use of partly or completely neutralized hydroxyaryl fatty acids as corrosion inhibitors. Although they have a good corrosion-inhibiting effect, they are not readily accessible.
The use of carboxylic acids as corrosion inhibitors, for example in cooling lubricants, cleaners and corrosion-inhibiting emulsions, is widespread in the prior art. For example, DE-A42 29 848 describes a cooling lubricant emulsion of which the corrosion-inhibiting system is based on a combination of long-chain fatty acids, short-chain fatty acids

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